In general, a video signal recording apparatus comprises a mechanical part for driving a record medium, a servo circuit for controlling the mechanical part, and a video signal recording circuit for treating a video signal to be proper form for being recorded on the record medium.
A conventional video signal recording circuit has a constitution of a circuit shown in FIG. 1, and the circuit shown in FIG. 1 is a video signal recording circuit for a broadcasting system of a National Television System Committee (hereinafter, referred to as NTSC). Referring to FIG. 1, an automatic gain control (hereinafter, referred to as AGC) circuit 10 which receives a video signal through an input terminal IP, automatically controls the gain of the video signal, in order to maintain a constant level of the video signal. A first low pass filter 11 detects only luminance signals distributed in the frequency band below 3 MHz among outputs of the AGC circuit 10. A clamping circuit 12 clamps a luminance signal received from the first low pass filter 11 to a predetermined level, in order to suppress the level variation of the luminance signal. A detail enhancer 13 and a sub-emphasis circuit 14 which are connected in series to the output terminal of the clamping circuit 12 emphasize a high frequency component in the band of 3 MHz to 4 MHz among the levels of the clamped luminance signal which is the output signal of the clamping circuit 12. A main emphasis circuit 15 emphasizes the output signal of the sub-emphasis circuit 14 regardless of the level. A dark-and-white clipping circuit 16 restricts the maximum white level and the reference black level of the output of the main emphasis circuit 15, for example, the maximum white level corresponds to the 200% value against the video signal level of 140 IRE, and the reference black level 45%. Further, a first modulator 17 frequency-modulates the output of the dark-and-white clipping circuit 16 with the carrier wave signal which has a central frequency of 3.4 MHz with a variation of 1 MHz, and then supplies the frequency-modulated luminance signal to a high pass filter 30. The high pass filter 30 gets rid of low frequency components of the output of the first modulator 17, and then supplies the output to a mixer 40. On the other hand, an automatic color control (hereinafter, referred to as ACC) circuit 20 maintains the level of the burst signal among video signals received through the input terminal IP. A band pass filter 21 removes frequency components except 3.58.+-.0.5 MHz among outputs of the ACC circuit 20 and then supplies the outputs to a second modulator 22, in order to detect chrominance signals distributed in the band of 3.58.+-.0.5 MHz, which corresponds to the luminance component removed signal among outputs of the ACC circuit 20. A second modulator 22 converts the frequency of the output of the band pass filter 21 to be an amplitude-modulated signal in a band of 629 KHz. A color detecting circuit 23 checks the existence of a chrominance signal among the outputs of the ACC circuit 20, and then generates a color detecting signal having a predetermined logic, according to the result of the check. An automatic color killer (hereinafter, referred to as ACK) circuit 24 transmits or shuts off the output of the second modulator 22 to the second low pass filter 25 according to the logic state of the color detecting signal supplied from the color detecting circuit 23. The second low pass filter 25 removes frequency components above 1.2 MHz among the outputs of the ACK circuit 24 and then supplies the outputs to the mixer 40. Then, the mixer 40 mixes the output of the second low pass filter 25 and the output of the high pass filter 30 and then supplies the mixed output to a head HD through a recording amplifier 50 and the head HD records the converted video signal, which is supplied from the mixer 40 through the recording amplifier 50, on a record medium.
If a color video signal consists of a luminance signal having a bandwidth of 0 to 3 MHz and a chrominance signal in a frequency band having a central frequency of 3.58 MHz with a deviation of 0.5 MHz, the luminance signal is frequency-modulated to have a carrier wave frequency of 3.4 MHz with a deviation of 1 MHz with respect to the video signal having a maximum white level of 140 IRE, and the color signal is low-frequency-converted to a signal the amplitude of which is modulated in a band of 629 KHz.+-.0.5 MHz as shown in FIG. 2B. In this case, since the frequency-modulated luminance signal and the low-frequency-converted chrominance signal are overlapped at near 1 MHz as shown in FIG. 2B, both signals affect each other. The above mentioned cross talk between luminance signal and chrominance signal cause the luminance and color beat, so-called moire phenomenon, on a screen during reproducing. To prevent this phenomenon, in a conventional video signal recording circuit, low frequency components of the luminance signal around 1 MHz affecting the chrominance signal are removed by a high pass filter 30, and high frequency components of chrominance signal components around 1 MHz which affects the luminance signal around 1 MHz are removed by a second low pass filter 25. However, in the circuit of FIG. 1, if the cut-off frequency of the high pass filter 30 is shifted to a high frequency, an outline of a screen is destroyed and a horizontal resolution is deteriorated, on the contrary if the cut-off frequency is shifted to a low frequency, the above-described beat phenomenon is occurred. Furthermore, in case that a black-and-white image signal including only a luminance signal having a band 0 to 3 MHz is supplied to the input terminal IP in FIG. 2A, the black-and-white video signal is frequency-modulated as the luminance signal of the color video signal, and then filtered, so that the image of fine contour resolution can not be reproduced.
As a result, in the conventional video signal recording circuit, the color balance is not exactly balanced in a color video signal recording, and only luminance components of high frequency components are removed, so that a fine image can not be reproduced in a black-and-white signal recording.